1. Field of the Invention
This invention relates to a training method for a non-nyquist transmission system and a training data transmission apparatus for a non-nyquist transmission system.
2. Description of the Related Art
Various modems (modulator-demodulators) for use for transmission of data which can transmit data at various transmission rates have generally been provided.
For example, modems for the transmission rate of 9,600 bit/sec according to the Recommendation V. 29 adopt, as a transmission system therefor, the Nyquist transmission system. Here, according to the Nyquist transmission system, signal points arranged at Nyquist intervals (Nyquist frequency (refer to FIG. 10(a))) on the time base are transmitted at the Nyquist intervals, and signal points can be transmitted without inter symbol interference with any other signal point.
Further, upon transmission of data, a modem modulates and transmits training data of a required pattern prior to transmission of the data, and the training data are demodulated by a demodulation section. Then, using the thus demodulated training data, initialization processing of a reception section of the model is performed.
In particular, a reception section of a modem includes, in addition to a demodulation section, a roll-off filter, an automatic gain control section (AGC), an automatic equalization section (AEQ), a carrier phase correction section (CAPC), a timing extraction section, a carrier detection section and so forth. Upon starting of transmission of data, those sections must be initialized. Optimum signals necessary for such initialization processing are: for example, a tone signal for the automatic gain control section; a tone signal or an impulse signal for the carrier phase correction section; .pi./.pi. signals (two signals having phases different by 180 degrees from each other) for the timing extraction section; and a tone signal for the carrier detection section. It is to be noted that, in order to perform initialization processing for the automatic equalization section, an impulse signal is regenerated and used for the initialization processing.
Thus, training data of a required pattern are sent prior to transmission of data so that such optimum signals (optimum pattern) as mentioned above may be supplied to the various sections of the reception section of the modem.
An exemplary one of training patterns (training data) which satisfy the requirement described above is illustrated in FIG. 15. Referring to FIG. 15, the training pattern 100 shown has a first repeat signal portion (SEG2) 100a in which signals A and B whose signal points have phases different by 90 degrees from each other are arranged alternately, and a multi-value random signal portion (SEG3) 100b which is positioned subsequently to the first repeat signal portion 100a and wherein signals C and D whose signal points have phases different by 180 degrees from those of the signal points of the signals A and B, respectively, and different by 90 degrees from each other are arranged at random. It is to be noted that, subsequently to the multi-value random signal portion (SEG3) 100b, scramble Z (SCRZ) signals (refer to SEG4) obtained by scrambling Z-polarity data in transmission data are sent, and thereafter, data (refer to SEG5) are sent.
If signal points on a phase plane of the signals A to D mentioned above are denoted by the same reference characters as those used to represent the signals, then the arrangement of the signal points of the signals A to D is such as as seen in FIG. 16. Referring to FIG. 16, the signal points A. B. C and D are displaced by 90 degrees in phase from each other.
Since a tone component and a .pi./.pi. component are included in the training signal of the ABAB . . . pattern, a tone signal and .pi./.pi. signals can be regenerated by suitable operation processing of the training signal. Further, from the CD random signals, a flat spectrum is obtained to perform adjustment of the automatic equalization section.
By the way, in recent years, very high speed modems having the transmission rate of, for example, 28.8 kbps have been proposed. Some of such high speed modems do not adopt the Nyquist transmission system but adopt a non-Nyquist transmission system. Here, the non-Nyquist transmission system is regarded as a transmission system by which signal points disposed between two Nyquist intervals are sent at Nyquist intervals on the time base, and transmits signal points with inter symbol interference with other signal points.
However, where such non-Nyquist transmission system is adopted, if a training signal which has generally been used in the Nyquist transmission system is used as it is, then a timing phase cannot be extracted by the reception section also because the non-Nyquist transmission system involves no Nyquist frequency.
Therefore, a modem which adopts a non-Nyquist transmission system requires a new training method which employs novel training data.
It is to be noted that also any other transmission apparatus than a modem which adopts a non-Nyquist transmission system similarly requires a new training method.